Technical Field
The present invention relates to an optical image measuring device for observing a measurement target using interference of light beams.
Background Art
In recent years, optical coherence tomography (OCT) has been drawing attention as a technology that can visualize the internal structure of a measurement target using interference of light beams. OCT has been widely used for funduscopy, and has been used to diagnose a variety of eye diseases. In recent years, the range of the application of OCT has expanded to a variety of fields, such as dermatology, cardiology, odontology, oncology, and food industry.
In OCT, as described in Patent Document 1, for example, a light beam from a light source is split in two that are a signal beam to irradiate a measurement target and a reference beam to be reflected by a reference beam mirror without irradiating the measurement target. The signal beam reflected by the measurement target is combined with and thus is caused to interfere with the reference beam, so that an interference signal is obtained.
OCT is broadly divided into time domain OCT and Fourier domain OCT depending on the method of moving the measurement position in the optical axis direction (hereinafter referred to as z-scan). In time domain OCT, z-scan is performed by using a low coherence light source as a light source and moving a reference beam mirror during measurement. Accordingly, only the components in a signal beam that have the same optical path length as the reference beam will interfere with the reference beam. Performing envelope detection on the obtained interference signal can obtain a desired signal through demodulation. Meanwhile, Fourier domain OCT is further divided into wavelength-scanning OCT and spectral domain OCT. In wavelength-scanning OCT, z-scan is performed by using a wavelength-scanning light source capable of causing the wavelength of an emitted beam to scan, and causing the wavelength to scan during measurement. Performing Fourier transform on the wavelength dependence of the detected interference beam intensity (i.e., an interference spectrum) can obtain a desired signal. In spectrum domain OCT, using a broadband light source for a light source, splitting a generated interference beam with a spectroscope, and detecting the interference beam intensity for each wavelength component (i.e., an interference spectrum) correspond to the z-scan. Performing Fourier transform on the obtained interference spectrum can obtain a desired signal.